[3] Musically, "#Cookie Jar" was described as a song that has "groovy bassline and uptempo, twinkling electro-pop melody" that recalls Rookie.
[4] Following its initial release, "#Cookie Jar" was met with mixed reviews from music critics.
Lee Gi-eun of TV Daily called the track "addicting", further adding that "even if you only listen to it once, the merriness of the Red Velvet songs is there".
[4] The music video features the group members dressed in cute pastel-style outfits and original accessories, showing off unrealistic comic visuals.
[6] Tamar Herman of Billboard noted Red Velvet's "similarly bubbly, bathing the fivesome in retro looks inspired by the '60s, '70s, and '80s" music video theme.